I just installed the elevators with the pull-pull setup on my DP Edge and I am using a single servo as instructed in the manual. The control horns are shifted to the right (when looking from the tail) as the manual instructs and the servo should be offset to the right as well.

The problem is with both elevators neutral and the servo horn 90 degress from the servo, the each half is centered, but when I move to the extremes, one leads and the other lags. Any suggestions?

thanks
Erick

I have the same probleme with my cap 232. It's because the servo moves in one direction and pushes more on one part of the elevator. Be sure that the pushrod from the servo is straight.
Chris

JR & Futaba transmitters will have this problem when you mix channels. I am not sure exactly why this is so, but is has something to do with how the packet of information is put together and transmitted to the receiver.

What I have done is adjusted the end points and linkage to get the controls to track evenly though the entire range of motion when the controls are moved slowly. This seems to help. Also using high speed servos help as well (digitals are great).

To fully eliminate this problem a matchbox or reversible "Y" can be used. I don't like using these but I know of several people who do.

Eric, A friend had the exact same problem with his DP Edge. His solution was to put the servo in the middle of the fuse and to move the control horns on the elevator so that they were even and not off to one side.

This sure worked for his Edge.

Why not just use 2 servos in the elevator for better control surface authority?

You may also have to adjust where your linkage is connect to the control surface to make sure that the throw is the same.

Hey Guys

Thanks for the feedback. Here is where I am at.

I am using one servo to try and keep the plane as light as possible. Besides, I think a 125 oz digital should have enough pulling power or both halves. In theory, the pull pull seems like it would work fine, but for some reason, then the servo arm moves it is pulling one half more than the other. I moved the servo from the right side, like they show in the picture, to the center like Edgeguy suggested. I was sure this would fix it.... NOPE[] It still responds the same way.

I would love to know if anyone is successfully using the double pull-pull for the elevator on this plane. If so, how in the heck did you make it work without having any difference in elevator travel?

As a last resort I could use two servos, but I would really like to get this to work. I do not think Dave Patrick would suggest doing it this way if it has a known problem. I am sure that I have something setup wrong, perhaps with the geometry.

Marc (RCAdmin) suggested putting the elevator servo on its side so the servo arm is in the center of the plane and in a vertical position. He thinks that this way the arm will always move in the center line of the plane rather than swinging to the left and right causing it to pull at a different angle on one half than the other.

How are you guys setting up your elevators?? HELP

Can you post pics?

Thanks
Erick

Turning the servo on it's side is without doubt the best place but nothing repeat nothing will cure your (and everyone elses) problem unless the lenth of the horn (from the control surface center, ie hinge point to the clevis hole) is exactly the same lenth as the servo arm (from the center screw to the clevis hole).

These dimentions can be as short or as long as you like it... simple dosn't matter as long as they are both the same length! The concept of placing the clevis futher out on the servo arm to increase throw dosn't work with pull-pull.
There is only one throw, max inboth directions and this must and can only be achieved successfully with equal servo arms and control horns.
All increases and reduction of throw are controlled from the ATV function or similar on the transmitter.

This will cure your problem.
Enjoy the aeroplane.

Eric, sorry but I gave you some false info. My friend only moved his servos rudder and elevator both as close to center as possible. Rudder on left side of fuse and elevator on the right side. But he did change some of the control horns on the elevator. He purchased a matched set of sullivans so that all control horns were positioned evenly on the elevator. This works perfectly now. Here are some pics.

Here are a couple of extra pics. This is powered by a Mki 2.10 and flies great.

May I also add that exit slots on the fuselage sides should also allow unimpeded motion of the wires.

I'm using a pull-pull on my Extra. The servo is centered in the fuse and the horn on the servo is much shorter than the horns on the elevator. I was very careful about laying-out and cutting the exit openings as well as making sure all four cables were tensioned equally. If would be very difficult to eliminate all the geometric problems with this control configuration. To do so requires that every angle on all four cables and all the horns be exactly equal. Good luck.

If all your geometry is basically correct, and nothing strange is happening in the exit openings, I would check cable tension. I did this by plucking them like a harp string. They should hum at the same frequency.

Erick:

Putting the servo on it's side so that the arm is vertical in the center of the fuselage will solve the problem you mentioned.


Bla Bla:

The set up you discribe is only required if the pushrods are rigid. (Otherwise known as a push/pull system.) In a pull/pull system the cable opposite the pulling cable is expected to go slack.

Jim

Erick, I have the pull-pull on my edge and it works FINE. One thing to consider is centering the servo (subtrim) so that the arm is at more of a ninety degree pull to the horn. What I mean is set it so that it is NOT perpendicular to the fuselage, but at a little bit of an angle. That may work.

I used deflection meters when I set min up and there is NO measurable difference between the halves at any elevator position.

Well Guys, I figured it out. The problem that I was having was a matter of the incidence on one stab not matching the other one. A friend came over to night with a fresh set of eyes, and we resetup all the connections to the elevator control horns with the elevator servo in the center of the tray. With the leading edge of the counter balance lining up with the leading edge of the stab on each side, we thought each half was even.

WRONG! When looking at the trailing edge of each elevator half, there was noticable difference on how they lined up. I put a Robart Incidence meter on each and realized that the right stab was off. WE adjusted the stab and now both elevators move the same.

The problem is that there should have been a mention in the instructions to use an incidence meter on the stab before the elevators are glued in position.

Thanks guys for all your help and comments.

Erick

Ah. I also noticed that the instruction for the Extra are vague on this point. I have always got by without and incidence meter. Maybe that will have to change now.

Jrf bro... just so you have the terms correct for future use:
one solid pushrod is called a push-pull setup.
A pull-pull setup can have cable or solid push rods.

Also your reference to the fact that one cable is "expected to go slack" on a correct pull-pull setup is again totally incorrect. Any reference to the word "slack" used in an aerobatic context should be seriously reconsidered as this will only create problems.

Most of us spend a great amount of energy eliminating "slack" at all cost, be it incorrect pushrods, clevis's, servo gears, hinges etc etc. I suggest you should try doing the same...it make quite a difference.